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What is the minimum bank angle that an older aircraft like the Cessna 172 can apply in a coordinated turn?
Suppose the weather conditions are favorable and there are no significant winds. The Cessna with a speed of 200km/h starts a coordinated turn with a bank angle of 0.1°
The turning radius of this trajectory would be 180km. (a circular perimeter of 1130Km)
Would it be feasible to apply and hold such a small bank angle to draw such a circle?
When I say feasible, I mean that if there is a possibility that an old aircraft may set a bank angle as small or less than 0.1° in its controls.

why do you think it would not be feasible? (usefullness aside)

Just draw the circle on your sectional chart and fly it, keeping the ball centered.  Your average bank angle will be 0.1 degrees.

This would be entirely theoretical. In reality you will have to compensate your turn for winds aloft so sometimes you would have a much higher bank angle to "draw" a circle on a map.

When I say feasible, I mean that if there is a possibility that an old aircraft may set a bank angle as small or less than 0.1 ° in its controls.

"possible to do easily or conveniently..."  Definite no.  What are you actually trying to do?  There's probably a better way.

While it would be possible to perform the intent of flying a fairly precise arc of 180 km radius (depending on your degree of tolerance), it would not be possible to maintain a precise bank angle of 1° during the entire arc. Regardless of the age of the aircraft. There are too many other factors that would influence the bank angle. Factors such as lateral wind movement, up/down drafts, thrust, airspeed, groundspeed, differential weight, lift and load factors, etc. Even after trimming out the aircraft, these factors would be constantly changing over time.

Dean, he asked about a tenth of a degree!  P.S.  There is a word for this kind of question - a very precise question about a solution you may have already decided on that is not even the best solution to the root goal...  If you help us understand what you are trying to accomplish you will probably get a flurry of good ideas.  Meanwhile I am going to add to the downvotes because the question doesn't show much forethought.

In the FAA manuals there is no indication of the maneuver that a pilot must perform to avoid drift caused by the rotation of the earth known as the Coriolis effect. Outside of the FAA manuals there is this proposal: http://walter.bislins.ch/bloge/index.asp?page=How+Airplanes+correct+for+the+Coriolis+Effect Said proposal would imply that the Spirit of St Louis to reach its destination would have required a bank angle of 0.0025 ° sustained throughout its trajectory.

@MichaelHall - How would you even measure a tenth of a degree of bank? Let alone trim the aircraft for it. Like you, I wonder about the practical purpose of measuring a bank angle that precise. It would be easier and more practical to just to fly a 180 km DME arc (if it can be programmed as such in the OP’s particular aircraft)

@ElpéndulodeMoisés - There would be no reason to maintain a bank angle of 0.0025° over a transatlantic distance. To give you some perspective, a 0.0025° course deviation would put you off course by one mile over a 24,000 mile course. This is not an exact comparison because 1° bank angle does not exactly equal 1° course deviation. At altitude, I can see a landmark below me offset by more than 1 mile. Even by clock and compass, CL would have plenty of time to correct in a no wind situation. Luck was on his side.

PS. The reference you cited has this to say, “This bank angle is not noticable. The pilot or autopilot applies this bank angle automatically as he is constantly correcting for any deviation from the planned track. There is no need to plan for such corrections, because they are too small to have any influence on the flight calculations and the necessary corrections for crosswind are bigger and unpredictable.”

What is the significance of the term "old aircraft"?

Modern aircraft tend to have more sensitive bank angle displays. Older aircraft do not

So is this question actually about the Coriolis effect, or are you just using it as an example?  Coriolis effect affects winds, winds affect pilots.  Otherwise we don't care about, or compensate for Coriolis in the way we fly our airplanes.  Ever hear the expression "measure with a micrometer, mark it with a crayon, and cut it with an axe"?

@ElpéndulodeMoisés - Correction, newer avionics tend to be able to be calibrated more precisely. It has nothing to do with the age of the airframe. Aircraft avionics are constantly being retrofitted. On the other hand, the visual display commonly used by the pilot is very standard. The pilot would not see the fine tuned calibration. A pilot flying steam gauges or glass panels would only see a rough indication of bank angle from which they would determine their attitude.

Case in point. There are 10° & 20° marks on my Attitude Indicator. At my aircraft’s airspeed, I can guess through calculations and know through trial and error to place my bank indicator just a hair past the halfway point of the marks to affect a standard rate turn. But, I can not rely on that alone. I have to cross check that with a clock and a Directional Gyro (compass if necessary). And, that is with modern avionics.

No, it is not feasible.  It is not feasible to sustain 1 degree of bank, let alone one tenth of that.  There is no angle of bank indicator that precise, and even if there were it is not possible to maintain that level of accuracy for such an extended period of time.
For an example, ask yourself this:  is it "feasible" for you to hold your fingertip exactly .001" from the tip of your nose for 2 hours?  (Maintaining an air gap, not using a feeler gauge...)  Of course not.  It is not realistic to expect that kind of accuracy and inevitably you would sometimes touch.
However, you can reasonably meet the intent of keeping your finger fairly close.  Or of flying a fairly precise arcing ground track if that is your goal.
For another example, assuming you have a driver's license and drive on high speed interstate highways, pay attention the next time you are on a gently arcing curve and see how much your steering wheel actually moves to hold the road.  It doesn't.  Not perceptibly.  Not at 60MPH on a very gradual bend in the road.  You simply hold it steady and make miniscule adjustments to stay in your lane.
Same thing in an airplane.  You cannot hardly even detect one degree of angle of bank, you simply make fine and continuous adjustments to maintain track.  (And sometimes a degree or two of bank is needed just to keep a straight course!)
As it has been pointed out, you are looking at this backwards:  It is very easy to fly an arcing path, but you wouldn't do it in the manner you suggest.

Yes.  Humans, and probably most other animals, usually don't maintain precise anything.  They work by feedback, constantly correcting position &c.  It's the same as maintaining say a 10% bank angle: you constantly apply minor corrections.

@jamesqf . . . . the difference being that 10deg + or - 1deg is still 9deg to 11deg but 0.1deg + or - 1deg is +1.1deg to -0.9deg and -0.9 means you're banked and turning in the opposite direction.

Thanks for answering. I have heard that even in conditions where there are no crosswind components in straight and level flight, commercial aircraft must constantly move the nose 1 ° or 2 ° to the right and left. This is also done by banking to make small coordinated turns or only with the tail rudder? And what is the purpose of this maneuver?

If you try to drive a car or ride a bike in a straight line you will need to make small adjustments, right?  You cannot just freeze things and expect it to track perfectly straight.  Or move the steering wheel once and hold it steady, expecting to perfectly track a curve in the road with no additional corrections needed.  Why do you think it would be any different in an airplane?

There are many differences in the physics of a car moving on a road and in the physics of an airplane moving through the air mass but I agree that corrections are necessary. I just wanted to know if this type of correction had a specific name and what would happen in practice if this horizontal movement of the nose is avoided for a certain time (obviously in ideal atmospheric conditions). So, assuming these constant corrections were unavoidable, I suppose that would be another reason why it would be unfeasible to sustain a 1 ° bank angle for long, even without considerable crosswind components

The corrections are called "staying on course" and "staying on altitude.  Yes, I know there is more to flying than driving a car.  I was trying to explain in a context that a non pilot could relate to.  (I assume you are not a pilot...)

@El péndulo de Moisés: I've no experience of commercial aircraft, but in a small aircraft like the 172 (especially older ones) there is probably more than one or two degrees of play in the control cables & bearings of the ailerons & rudder.  Just as there's play in your car's steering: if you're stopped, you can turn the steering wheel through some angle without moving the tires.


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Are civilian/GA pilots expected to "see and avoid" fast military jets in VMC?
I don't know if this also applies to the U.S. or just to Europe, but in Europe the civilian airspace is frequently used by military jets. On numerous occasions I've seen F-16's and other fighter jets using the same airspace I was flying in (both controlled and uncontrolled)
According to the regulations, we should "see and avoid" other traffic but does that rule apply when encountering these fast military jets? Let's face it: there's no way you can see and avoid a fighter jet approaching at +400kts.
Are there specific regulations covering this? Who's at fault when a midair collision occurs? (sadly it has happened in the past)
EDIT
It happened again last week: https://en.wikipedia.org/wiki/2015_Moncks_Corner_mid-air_collision
How can something like this happen? Don't F16's have their own radar?

Below 10,000MSL there is a speed limit of 250kts anyway with the exception of Military Operating Areas (MOA) that are depicted on the charts. http://www.cfinotebook.net/notebook/airspace/military-operating-area.html Makes me feel better anyway since I fly small airplanes usually below 10k

http://www.youtube.com/watch?v=qLVtstYAZLY

@p1l0t Actually that speed limit is waived for military aircraft on MTR's (see the 2nd excerpt in my answer below).

Yes I'm aware of this. I did forget to mention though.

@Lnafziger - as well as being waived for certain aircraft which are unsafe to fly below 250 kts for long periods, such as the T-38

@SSumner: Why is it unsafe?  Do they really have a stall speed greater than 250kts?

@Sean see this Q&A: https://aviation.stackexchange.com/questions/34480/what-aircraft-fly-faster-than-250-knots-indicated-airspeed-under-10-000-feet-for (essentially lack of control below 250 kts)

It is both parties responsibility to see-and-avoid, but it does help to know where you are more likely to find high speed military activity and high performance maneuvering to aid you in seeing and avoiding.
Military operations in the US are typically confined to military training routes (MTR), military operations areas (MOA), restricted airspace and prohibited airspace.
The MTRs are low altitude, high speed routes and are charted on sectional charts so you know to be extra vigilant around them or to just avoid them altogether.
Military operation areas or MOAs are charted and are big boxes with ceiling and floor altitudes.  GA aircraft can query ATC if these are active and in any case they can fly into them.  If a GA aircraft penetrates and active MOA, the military activity is typically stopped until you leave.  General rule of thumb is to just not go there.
Restricted areas are only accessible to you when cold, so there will not be military activity there if you allowed to be there.
Prohibited airspace may not have military activity before you show up, but certainly will after you do, and you might get to watch an F16 attempt slow flight and form up on your wing.  Remember your intercept procedures for this one.
Any military activity outside of this will generally be typical enroute flying at altitude.  You will occasionally hear ATC coordinating mid-air refueling but that won't be something you have to worry about.

This is certainly not the case in Belgium. Our home was located in G-airspace and we regularly saw F-16s buzzing overhead at 500ft AGL. It's definitely not a military training route.

@PhilippeLeybaert Yeah, the U.S. has a lot more wide open space in which the military can practice than most Western European countries, especially Belgium. If you look at sectionals of almost any state in the Western or Central U.S., there are MOAs (and/or restricted areas) everywhere.

Yeah, there's a big one down south of Abilene, called the Brownwood MOA, where most of the guys stationed in Texas go to play. It's no more than an hour's cruise time from JB San Antonio, NAS-JRB Ft Worth and Dyess AFB.

Yes, both pilots are required to see and avoid at all times when operating in VMC conditions.  Typically the military pilots have radar used to pickup other aircraft that can help them, but ultimately it still comes down to looking outside.
We have military training routes charted here in the US that are used by military aircraft when operating at high speeds, and pilot should be especially vigilant when operating in the vicinity of one of these routes.  Use all available information: Get flight following and  contact the frequency on the chart for current operational information, and above all keep an eye out for them!

The Aeronautical Chart Users Guide shows an example of how they chart it on VFR Charts:

Military Training Routes (MTRs) are shown on  Sectionals and TACs.
  They are identified by the route  designator: . Route
  designators  are shown in solid black on the route centerline,
  positioned along the route for continuity. The designator  IR or VR is
  not repeated when two or more routes  are established over the same
  airspace, e.g., IR201- 205-227. Routes numbered 001 to 099 are shown
  as  IR1 or VR99, eliminating the initial zeros. Direction of  flight
  along the route is indicated by small arrowheads  adjacent to and in
  conjunction with each route  designator.
The following note appears on Sectionals and TACs  covering the
  conterminous United States.

There are IFR (IR) and VFR (VR) routes as follows:  Route
  identification: a. Routes at or below 1500’ AGL (with no segment
  above 1500’) are identified by four-digit numbers;  e.g., VR1007, etc.
  These routes are generally  developed for flight under Visual Flight
  Rules. b. Routes above 1500’ AGL (some segments of  these routes may
  be below 1500’) are identified by  three or fewer digit numbers; e.g.,
  IR21, VR302,  etc. These routes are developed for flight under
  Instrument Flight Rules.
MTRs can vary in width from 4 to 16 miles. Detailed  route width
  information is available in the Flight  Information Publication (FLIP)
  AP/1B (a DoD  publication), or in the Digital Aeronautical Chart
  Supplement (DACS) produced by AeroNav Products. Special Military
  Activity areas are indicated on the  Sectionals by a boxed note in
  black type. The note  contains radio frequency information for
  obtaining area  activity status.

On IFR charts, they are similar:

MILITARY TRAINING ROUTES (MTRs)
Military Training Routes (MTRs) are routes established  for the
  conduct of low-altitude, high-speed military flight  training
  (generally below 10,000 feet MSL at airspeeds  in excess of 250 knots
  Indicated Air Speed). These  routes are depicted in brown on Enroute
  Low Altitude  Charts, and are not shown on inset charts or on IFR
  Enroute High Altitude Charts. Enroute Low Altitude  Charts depict all
  IR (IFR Military Training Route) and VR  (VFR Military Training Route)
  routes, except those VRs  that are entirely at or below 1,500 feet
  AGL. Military Training Routes are identified by designators  (IR-107,
  VR-134) which are shown in brown on the  route centerline. Arrows are
  shown to indicate the  direction of flight along the route. The width
  of the route  determines the width of the line that is plotted on the
  chart:
Route segments with a width of 5 NM or less, both  sides of the
  centerline, are shown by a .02” line.
Route segments with a width greater than 5 NM, either  or both sides
  of the centerline, are shown by a .035”  line.
MTRs for particular chart pairs (ex. L1/2, etc.) are  alphabetically,
  then numerically tabulated. The  tabulation includes MTR type and
  unique ident and  altitude range.

As far as who is at fault, it is a joint responsibility so everybody would be in most cases.

There's no way you can see and avoid a fighter jet at speed.

Sell your 172 and buy a war-surplus F-4.

Quite the opposite, I regularly am flying directly at another jet with a closing speed of greater than 900 KTS and can see them quite well.  Not for very long, but I can see them.  :)

@Lnafziger I'm sure you can, but you probably knew where to look.

@PhilippeLeybaert Sometimes, but not always!

@Lnafziger; fighter jets (as opposed to other jets) are usually painted in a way to.. well.. make them hard to see, aren't they?

@roe Yes they are, but that doesn't change the regulations, unfortunately.....

Lo these many years ago, the US Navy had a poster up for flight safety. It stated, " At today's jet speeds, the time involved from seeing an oncoming aircraft to the time the pilots can almost react is short."

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How are fighter jets allowed to be flown by one pilot even with maximum take off weights exceeding 12,500 lb?
I know that planes that are under 12,500 lb MTOW can be flown by a single pilot. But what about fighter jets like the F-18 and F-35 that way exceed that. For instance, the F-35 has a max takeoff weight of 60,000 lb.

Isn't number of pilots more related to the mission workload the plane is made for than the plane's weight? I don't see how the number of pilots has anything to do with the weight.

@757toga I see.

Seeing as we already have unmanned aircraft ("drones") I don't see why you're asking this.

@CarlWitthoft It's a regulatory question, but this wasn't at all clear by how it was phrased unless you already know it's a regulatory thing.

Who's gonna stop them?

Might help if someone would [edit] this question to clarify that it's about regulatory requirements.

So it's explicitly not about [tag:aircraft-performance]? And maybe "able to" in the title should be changed to "allowed"?

There are actually two different answers to this question.
First, your information that all airplanes over 12,500 lbs. must have two pilots is outdated. Now, while most such planes require two pilots (per FAR 91.153), it's entirely possible for specific planes to be type rated for just one pilot. For instance, the Pilatus PC-24 has a MTOW of 18,300 lbs., but is certified for single-pilot operation.
The second is that the military isn't actually under the jurisdiction of the FAA. So, even if the FAA still required two pilots for all aircraft over a certain weight, that wouldn't apply to a military aircraft.

@757toga Nice. FAR 1.1: https://www.ecfr.gov/current/title-14/chapter-I/subchapter-A/part-1#p-1.1(Large%20aircraft)

Given that we now have planes with zero pilots (or at least, zero pilots in the cockpit - they may or may not be controlled by someone on the ground), it makes sense that those rules would have changed...

@757toga I said that because I'd searched the rules, and found an article that said the rule no longer applies. Didn't find the FAR, though. I've edited the answer.

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What airplane is this guy sitting in?

What airplane is this guy sitting in?

+1 for “this guy”.

wait... is it https://i.sstatic.net/Ep2ss.jpg ?

@uhoh No, wrong side of the Atlantic.

That is an Airbus A400M Atlas. Here is a picture for reference:

(Wikimedia Commons)

The airplane is an Airbus A400M  Atlas (credits to Bianfable)
The airport is Farnborough Airport
The guy is the (soon to be former) Prime Minister of the UK, Boris Johnson. He opened the Farnborough air show

*for some values of "soon" :)

6th of Sept is the generally accepted date https://www.theguardian.com/politics/2022/jul/20/tory-leadership-race-final-two-what-happens-next-conservative-party-members


text:
Lateral balance of single aisle planes with odd numbers of seats in each row
Do single aisle passenger planes with an expected odd number of seats in each row (e.g. 2-3, 1-2) where the aisle ends up not being central adjust the design of the plane overall to account for this and if so, how?  If the plane later gets deployed in a cargo capacity does much need altering based on the above?

In a 1 - 2 seating config, with a full aircraft, the off center weighting of the PAX is not that far off the absolute centerline. Maybe 18". Easily handled by trim settings.

In all of my years of flying only once did I experience a flight attendant asking some passengers to move for weight and balance reasons. It was a commuter turboprop, probably about 35 passenger size, but there were less than ten of us on the flight. Naturally everyone had selected seats near the front. The FA asked for a few volunteers to move to either the middle or rear of the plane. To your point she said nothing about what side of the aisle to sit on.

@StevePemberton the distances are quite different in the longitudinal axis.

I've experienced that in 737s (again longitudinal rather than lateral). The flight had something like 10-20 passengers total.

@jcaron - "the distances are quite different in the longitudinal axis." Would you mind elaborating on that? ROFL


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How do autopilots maintain/adapt wind crab angle while flying a certain course over the ground?
How do autopilots maintain/adapt the wind crab angle while flying a certain course? With ailerons or rudder, or both?

I think this question betrays a certain misunderstanding of how airplanes fly. Autopilots do not "maintain a crab angle" nor do they un-co-ordinate the ailerons and rudder when flying in a cross wind.

Exactly that, the aircraft fly in relation to the air. Therefore all the autopilot has to do is to fly a different course relative to athmosphere such that the resulting course over ground matches the desired course over ground. To maintain this course relative to the atmosphere, no input is necessary.

Misunderstanding is being explored further here -- https://chat.stackexchange.com/rooms/142073/discussion-between-quiet-flyer-and-hans

As a general rule, it would be ailerons.  If I’m hand-flying and need to make a few degrees of course heading change to follow a course, I’m going to to do this coordinated, with aileron and rudder pressures that will often be imperceptible to an observer.  Making heading changes in cruise, even small ones, with a rudder skid alone doesn’t work well, so it will always be a tiny bit of aileron and an even tinier bit of rudder.
Also, most GA autopilots are two-axis autopilots that have no rudder servo and know nothing of the rudder.  Some autopilots provide a yaw-damper.  That’s a servo that automatically adds whatever rudder pressures are required so that the rudder is coordinated properly with the ailerons.  But again, a rudder skid is not a desired flight maneuver and not something an autopilot engineer would design into the system.  The autopilot would do the same thing a pilot would do, input a tiny aileron deflection and a simultaneous even tinier rudder pressure to keep the ball centered.

Your answer ist factually correct, but does not include that OP has a wrong understanding what a crab angle is or why it is necessary.

@quietflyer I am not sure, the questions asks "How do APs maintain [...] wind crab angle". For me this is enough to either ask the author to clarify or clarify this in the answer. Anyway, in doubt for the accused, I will remove my downvote.

@U_flow At first I thought the same thing and started typing something similar to that as part of my answer.  But the more I thought about it, the more I kept thinking “wait, ‘wind crab angle’ is exactly what someone would accidentally call ‘wind correction angle’ and didn’t imply it was held in as a control input.”  But your point is a good one and I’ll add it.

I've found that light pressure on rudder alone actually works pretty well for small heading adjustments in some light airplanes-- mechanism seems to be partially skid turn and partially slight change in bank via slip-roll coupling-- it's an interesting experiment to compare and contrast effectiveness of this method versus standard "coordinated" inputs when flying (with a safety pilot etc) in actual IMC with a "reverse hood" arranged so "guinea pig" pilot  can see only wet magnetic compass, no gyro instruments.  On a southerly heading (in northern hemisphere).  (Will delete shortly).

During IR training, I was specifically taught to make small heading adjustments (eg when keeping the needle centered) with rudder only to prevent over correction.

To clarify, my question was initially around the following. I fly from A to B. I'm at A. I have an ideal track line(route) to B, which is at the beginning identical to my desired CoG. Crosswind implies a Crab-angle, which changes over time, and which results in a x-track error. Bringing me back onto my ideal desired course and keeping it through changing winds, little maneuvers are necessary and probably some bias settings to ailerons(wing low) (and/or rudder) is necessary, keeping/regulating the ideal path. I wanted to know, if low cost GA type of AP use ailerons only, or rudder, or both.

@hans most lower-cost, entry-level autopilots will not have a rudder servo, and ailerons will be the only option.  Many GA autopilots are capable of providing rudder coordination (a yaw damper) but the cost of adding the additional rudder servo, or lack of existing certification for their particular model discourages most from doing it.  For instance, a rudder servo would be rare on a 172 or SR20, but more common on a Bonanza.

@Max R, yeah, that's what I thought, but I wasn't sure about. I think I also confuse 2 things. 1 is, regulating the controls to keep a certain CoG. 2nd is, in case of a x-track error to induce additional settings to regain the ideal track. Thank's for you answers, that's what I was looking for.

Hi, I'm flying an LSA(ULM) where my pilot weight introduces already a significant unbalancing of the CG to the left, if I'm flying alone. Hence, if I let the stick go, the ACFT turns immediately to the left. As a matter of fact during flight it is very hard to say if cross wind, weight or other issues force me to apply a constant bias to the ailerons due to the quick silverish behavior of such an LSA. Until now, I assumed that both would do; may be this was wrong. On the other hand, what about the technique flying "wing low" approaches during landing w/ crosswind to avoid drifting?

ct'd: Looking at it from an engineering POV. Ideal CoG 180°, low cost AP w/ 1 aileron servo. The AP knows nothing about wind; it can only measure the drift angle. When the ACFT flies 185°, the AP will bring the left wing low and steer the ACFT into an uncoordinated left turn, until 180° are reached. If the AP would then level off, the drift would start again, resulting in an oscillating course line along your desired track with an increasing x-track error. What an ideal regulator (PID) will do, IMHO is finding the ideal wing low position and keep it, to keep you on track.

This will most likely result in a combination of permanent wing low trim and a small crab angle. I agree, that ideally the ACFT would fly a combination of CoG & HDG in perfect trim and level off, but this is as far as I'm concerned impossible to reach w/ 1 aileron type of AP.

Let us continue this discussion in chat.

Hi Hans, your questions are interesting but it's best not to have long discussions in comments-- I'll post some further thoughts in the "chat" ( https://chat.stackexchange.com/rooms/142073/discussion-between-quiet-flyer-and-hans ) and may delete some of my comments above. Others are welcome to chime in there too--

Assuming you mean wind correction  angle, that’s simple: they don’t.
When in NAV mode, the autopilot‘s sole task is keeping the needle centered, and it will turn the plane (using ailerons, plus yaw damper if equipped) as needed to make that happen. It neither knows nor cares what the resulting heading is, much less complicated stuff like wind correction angles.
When in HDG mode, its sole task is keeping the heading bug centered, as if it were a NAV needle.  And it still doesn’t know or care about the actual heading selected, or what the winds are doing.

Might there not be some autopilots that use the aircraft's actual heading as one of several inputs when flying in "NAV" mode?  It seems possible to imagine some scenarios where that might be helpful (e.g. autopilot has just been engaged in NAV mode with aircraft flying on some random heading that is far from the desired ground track , winds are so strong that groundspeed is near zero and small changes in aircraft heading or airspeed or wind speed produce very large changes in resulting ground track direction, etc-- )

@quietflyer Anything is theoretically possible, of course, but I’m not aware of such.  Part of my pre-takeoff checklist is testing the AP (at zero GS), and it reacts the same way regardless of heading.  I suspect it’d misbehave with a negative GS due to reverse sensing, but no matter which way it turned, GS would soon go non-negative and it’d recover.

This isn't intended to be a complete answer, but rather to support other existing answers simply by pointing out that there's no difference in the techniques that would be used to maintain an appropriate heading in the presence of a crosswind (when a crab angle is required to maintain the desired ground track), and in the absence of a crosswind (when no crab angle is required.)  "Crabbing" is nothing more than selecting and maintaining a heading that is appropriately offset from the desired ground track, so that the actual ground track will match the desired ground track even in though there is a crosswind. "Crabbing" does not create a sideways flow in the relative wind over the aircraft, and so the control inputs required to maintain straight and level flight are no different when the aircraft is "crabbing" than when it is flying directly upwind or downwind, or when the aircraft is flying in still air.
It's not clear from the original question whether the asker may have some confusion around this point.
Thought experiment: an airplane is circling an untethered hot air balloon (at a safe distance), on a windy day, over a cloud deck, keeping a constant radius from the balloon, flying at a constant airspeed.  The airplane's flight path through the airmass is simply a circle, while the airplane's ground track cannot be.  Therefore at most points in the circle, the airplane's heading and ground track are different, which means the aircraft is crabbed.  Does the pilot have any way to tell at which points in the circle the plane is most crabbed and at which points the crab angle is zero?  Are different control inputs required at various points in the circle?  The answers are "no" and "no".
From the standpoint of the pilot, or the automated navigation system, the main consequence of a crosswind is that it creates a need to select a heading that is different than the desired ground track, and then evaluate whether or not the chosen heading is actually the correct one, and make further corrections as needed.  In the GPS era, that's a trivial task, and likewise for a VFR pilot simply following a road or railroad at low altitude.  On the other hand, when flying blind or above a cloud deck or far above the ground, without using modern aids such as GPS, the problem is far from trivial.  At any rate, such issues are completely different from the issue of what control surfaces are used to hold the desired course.

Further comments from O.P. suggest that this answer should be expanded to clear up one or two other misconceptions --


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Why is Landing Altitude displayed in amber on B777?
When I set the landing altitude manually, an amber LDG ALT and Landing Altitude EICAS message is displayed. There are no failures nor has the landing altitude been set incorrectly.
Why do I still get the EICAS message ALT LDG in amber?

The Boeing 777 is a very automated aircraft.  The takeoff altitude, landing altitude, and cabin pressurization altitude are all automatically set when you enter the departure airport and destination airport in the Flight Management Computer.
The EICAS message ALT LDG appears when the FMC is not controlling the landing altitude. This can be caused by one of three different conditions:
1) There is no destination airport entered in the FMC
2) The FMC landing altitude function has failed
3) The LDG ALT knob has been used to set the landing altitude manually
It is also normal to see ALT LDG after landing when the route has been dumped.

I used the knob to set it manually, but I thought if only the landing field value is incorrect, I will get amber light. --> so does this mean, I will always get amber light, doesn't matter if landing field is correct or incorrect ?

Yes, if you manually set the landing altitude, the amber EICAS message is telling you the FMC is not setting the landing altitude. You can clear the EICAS message but the underlying condition is still there and the message can be re-called to check the status.

thanks Mike for the answer, but what would be for example cause that FMC is not setting the landing altitude?

Not entering a destination airport is the most common reason, but malfunctioning software or hardware can also cause the FMC to not set the landing altitude.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


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Can we use MAYDAY or PAN PAN on ground?
Usually we read, on reports, aircraft reporting urgency or emergency during the flight, while airborne. But, is it correct to use these "words" on ground?

Real-life example: https://youtu.be/jIt6CDLrPOo?t=1m4s

Mayday on the ground can also be used to report danger to life somewhere else.  For example, you see an aircraft on fire in the circuit.  There has been no radio call.  Broadcasting a mayday stating what you saw and where is a proper procedure.

Emergencies can even be declared by non-aircraft, for example if a control tower needs to be evacuated for fire or other emergency.

http://atccommunication.com/mayday-versus-pan-pan  Give a good summary.  If it's immediate life-threatening, then "Mayday" would be proper on the ground too.

Yes, it is correct to use MAYDAY or PAN PAN PAN on the ground.
In recurrent training we are often reminded that in the case of a rejected takeoff in a foreign country it is important to use MAYDAY or PAN PAN PAN on the ground to avoid any confusion due to language difficulties.
It's probably a good idea at any airport as a disabled aircraft on a busy runway could be a major hazard to other aircraft landing and taking off.

And of course you want emergency services by you as soon as they can in basically all the cases you would need to use those words.

Absolutely they are correct to use on the ground if the situation warrants. They are used to express an emergency or urgency, and those can happen on the ground as well as the air. Those conditions are roughly the same: passenger illness requiring medical assistance, an engine fire, unlawful interference, etc.
When you make the call you would report your position as being on the ground, and where you are.

Another example of when Mayday would be appropriate while on the ground is when you've just crashed into said ground (e.g. runway excursion on takeoff or landing, crashing short of the runway, etc.)

@reirab - I suspect there wasn't much doubt that "If you crash, you can make a mayday call" :p that's pretty much the definition of an emergency

@JonStory True, but it is "on the ground," as the question asked. :)

I'd venture that if you're not on the ground, you probably haven't crashed yet

@JonStory Unless it was a mid-air collision (in which case you'll likely be on the ground soon.)

Ah but you said you'd crashed into said ground. Either way, definitely send a Mayday

Recent example: airplane lost directional control during landing rollout.


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Would it be possible to use 3D printed node based structures to make cheaper GA planes?
A car boasting 700HP and under the U.S LSA weight limit was just announced by Divergent Technologies. I was curious on peoples thoughts on using this technique in planes. Obviously there are some issues with the surface of the structure bearing load, but I imagine these could be overcome.

3D printing is unlikely to make anything cheaper in the near future. With current printing technologies it's an order or magnitude or two more expensive per unit than volume manufacturing techniques such as extrusion or injection moulding.
It's notable that the company you link to chose to make a supercar rather than a low-cost small car. There's little price competition in that market, as brand loyalty dominates. Most supercars are bought as status symbols or for fun rather than for their actual road performance. Most of the incumbents manufacture very small runs with a lot of hand assembly: exactly the kind of manufacturing that 3D printing is competitive for. On top of that, because of the status symbol marketing, there's huge room for new players to differentiate based on a green image. Tesla has done this in the last few years, which is why some of DMF's marketing material focuses on dissing electric cars.
Runs are small in GA too, so there's potentially a wider niche for these techniques to fit into. The market that would most closely fit IMO is kit aircraft. A kit that's primarily 3D printed parts joined by standard spars, with a flexible outer shell, could have shorter lead times and less tooling cost.

After discussing this with some mechanical engineer colleagues today, they pointed out how 3D printing of metals is now being used as a complement to CNC machining in the rocket industry. For a part that has to be machined from a single piece of metal, they 3D print a shell that's slightly larger than the required shape, and then machine it to the correct shape. It allows you to achieve the tolerances you get from machining (which 3D printing can't yet deliver), but without the waste you get from cutting down a solid block.
It's an aside to the main question, but it's a way that 3D printing could be used to reduce the cost of some components and allow designs that would have been economically infeasible.

If I read your first paragraph it seems like your answer is "no". But GA aircraft are, as you mention further down, produced in small numbers. It seems that 3D printing as a competitive production technology when the production volume is low. The lower tooling costs offset the higher unit costs. In the end your answer tends to be a "yes", but I am not sure.

@DeltaLima There's small numbers and small numbers. Even a run as small as a few hundred units can be a lot more expensive with 3D printing. While some 3D printing techniques could make even smaller runs feasible from a manufacturing point of view, it wouldn't reduce the one-off cost of designing and certifying a new type. That's why I say it could find a niche in kit aircraft, which mostly fly on a Permit to Fly rather than a type certificate.

3D printing is still an emerging technology. It's far from practical as a primary manufacturing method, but it is certainly possible as parts production - it is vastly cheaper to maintain a database of instructions than a warehouse of parts. Printers capable of making 1000cm$^3$ parts out of structural plastics like ABS are readily available on Amazon for $600. If you need bigger, the price goes up. A lot.
Airbus at one point was experimenting with 3D printing of sintered metals. If that ever works out it will revolutionise the spare parts industry, probably not in a good way.
As Dan said, kit and model aircraft will be early adopters.
Obligatory xkcd

I work at a company that routinely uses 3D printers for design of new components - although not for the aviation industry.  As the other posters have said, these parts are not cheaper than parts produced using other technologies.  However, our 3D printers have vastly increased the efficiency (and decreased cost) at which we can design new products.  Although 3D modeling of new parts in software goes a long way, being able to actually use the part in a prototype is a complete game changer.  And by printing out modified designs we can dramatically shorten the feedback loop to arrive at the "right" design.
I would suspect that use of this technology by aircraft manufactuers could therefore decrease the cost of design which might result in decreased costs overall.

The comments here are on point however I would like to mention that its very actively being looked into. GE successfully 3D printed a full working mini jet engine. That in and of its self is a pretty cool accomplishment. However it should be noted that the cost may not have been fully considered for that particular project.
GE also has at least one FAA cleared part that is 3D printed. It is a part for the GE90-94B jet engine.

The only kind of 3D printing process which produces structures fit for the load/weight ratios usual in aviation is electron beam printing. It uses titanium, stainless steel or aluminium grains (feels and looks much like sand) and heats that up locally to the melting point in an inert atmosphere, layer by layer. The advantages are:

Very fine structure, better than what is achievable by casting.
No molds.
Geometries which would be impossible to mold by casting or milling.

But there are disadvantages:

Rough surface; minimum roughness is given by grain size.
The surface imperfections translate into a notching effect, so the actually usable cross section is smaller than what is produced, which reduces material efficiency.
Manufacturing cost hardly goes down with the number of parts.

The only areas where this has been used gainfully so far are special cases:

Titanium implants, where replacements for bone structures can be custom-made within less than 24 hours. The rough surface is an advantage here, because it allows better integration into the body.
Replacement parts in case a JIT assembly line is compromised by one part missing.
Impossible geometries like hollow core pins for injection molding. The channels for the cooling water inside can have a corkscrew shape, one for the inflow, and one interleaved for the outflow. The gains in process efficiency can be immense.

In general, a 3D printed airplane is possible. Cost savings can be realized for a few special parts, but the general structure would certainly be more expensive. Consider that the surface roughness means that at least aerodynamic surfaces and contact areas with other parts need to be planed (e.g. by milling) after 3D printing.
While a single-issue sports car might be cheaper to produce this way, I very much doubt that GA manufacturing will benefit from 3D printing soon, even with the reduced production volume of today, except for some special parts.


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What are the advantages and disadvantages of ducted fans in designs such as the Airbus E-Fan?
I have read that it increases thrust and reduces noise. Is there a downside to this?

(Image source: Wikipedia)

Can you include a photo?

Not the best photo for the question, but it was the only free one I could find. See http://www.airbusgroup.com/int/en/story-overview/future-of-e-aircraft.html

technically a turbofan engine is a ducted fan

also did you read the wiki article on the matter

An answer to your question can be found here.
Advantages of ducted fans would be:

reduced noise
Better containment of broken blades
protection of ground personnel when the engine is running
Smaller size than a comparable propeller
They look like a fancy jet engine. This is probably the main motivation of Airbus for their use on the E-Fan.

For almost all aircraft designers, their drawbacks have weighed more heavily:

Less efficiency, because a smaller mass of air is used for propulsion
Additional friction drag and weight from the shroud

The highest propulsion efficiency is possible with a large, slow-spinning prop. Once flight speeds approach the speed of sound, the propeller has to become smaller to avoid supersonic propeller tips, and then the shrouded design becomes more attractive. Electric airplanes so far are not fast enough to profit from this effect. I would be very skeptical of the increased thrust claim - both efficiency and thrust of the E-Fan ducted fans are lower than what a well-designed propeller can offer.
The addition of the shroud only increases thrust when compared to the naked fan, but the fan is a poor replacement for a decent propeller at low speed.

Note that there is a difference between a gasoline engine and an electric motor - a motor produces more torque but is less effective at producing lots of "power" in the high-revs-high-horsepower sense of a "regular" engine. A ducted fan may be more effective at pushing a smaller volume of air "harder" than an engine, almost like a mini turbine with much higher angles of attack per blade than an equivalent propeller. This would be particularly noticeable at lower air/propeller RPM. I don't disagree with your answer, I just think we need to be careful not to directly equate a motor and an engine

@JonStory: No, the motor is not important here. What counts is the propulsion efficiency, and this is determined by the fraction $\frac{v_{\infty}}{v_{\infty} + \Delta V}$. For the same thrust, a smaller diameter will require a higher $\Delta v$, which results in lower efficiency.

I'm not talking about the efficiency of the propulsion at different velocity, I'm talking about the fact that a motor may be more efficient at a different velocity/power output to a motor. A large, slow propeller may be more effective, but it may be easier for an electric motor to turn a smaller fan faster: eg due to lack of gearing required, and the differing power delivery. That doesn't make a ducted fan better than a propeller, but it could reduce some of the disadvantages usually faced. Leaving more sway for the "It looks cool and is more marketable" factor.

@JonStory: OK, that way we can agree. I, however, would prefer if the E-Fan makes the best use of the little energy its batteries provide, and this would be by means of a propeller.

@JonStory: I don't think it has anything to do with the motor but rather with the noise, controllability (lower P-factor) and the fact that they probably do plan to develop it to aircraft flying at jet speeds. Electric motors have no trouble with low rpm.

@AnandS: Placing the engine inside the fuselage will create cooling problems. Generally, a larger propeller needs to spin more slowly, so a comparison at the same speed is not meaningful. Better to compare them at the same thrust, and then an unducted, larger propeller will be more efficient.

@PeterKämpf regarding the last sentence of your answer, how would you then define the difference between a fan and a propeller?

@Gabe Like a "real" fan, a fan in propulsion devices has a much higher activity ratio and a smaller diameter when compared to a propeller.

R W Hovey indicates Ducted Fans are more efficient below 100-110 mph, with 80 % propulsion efficiency (percent of delivered mechanical power that is converted to thrust), above this, a free propeller is better, 85 % efficiency from 200 to 300 mph, up to 400 mph, when it drops to 60 %, and is catched by turbofans, 64 % efficiency at 450 mph; above 500 mph, turbojet leads, but with a low 61 % efficiency, figures for jets start in 40 % at 300 mph.


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How should control surfaces be modeled in simulations?
I am modeling the lift and drag forces of a wing in software of my own creation.
If I have a wing which fits the profile of (for example) NACA 0024, it is a simple operation to look up the proper coefficients for lift and drag based on the current angle of attack for the wing.
But what happens if I slap an aileron on the trailing edge?
Do I need to re classify the wing based on the new geometry?
Should I treat control surfaces as their own aerodynamic bodies and look for lift/drag tables for them?
Since this is just a simulator, would it make sense to just offset the current coefficients by some value based on angle of deflection?
I am admittedly uneducated in aerodynamics and aviation, so please forgive me if I've come at this problem from entirely the wrong direction.
Any help or advice would be greatly appreciated!
Thanks!

Any control surface changes both local camber and local incidence, so it would be best if you change the coefficients accordingly. If you use a panel code, it would be enough to change the local surface inclination (= the flow direction at the local control point) by the deflection angle.
If you need formulas for the coefficients: A control surface with a cord length fraction d (of total chord length) will change the local lift coefficient $c_l$ with
$$\Delta c_l = \sqrt{d}\cdot c_{l\alpha}\cdot sin (\eta),$$
where $\eta$ is the deflection angle in radians and $c_{l\alpha}$ is the lift coefficient gradient over angle of attack of the original airfoil. The additional lift will act at a point between 50% and 25% of wing chord. The higher value is for very short flaps, the lower for all-flying surfaces (technically 100% flap chord), so a control surface deflection will add a torsional load. Drag will not be affected for small deflection angles, but when they get bigger, first drag rises and then the lift increase becomes nonlinear.
If you stay in the linear range (15° with 30% flap chord, 25° with 15% flap chord at moderate angle of attack) you can linearly add the flap effect (offset the coefficients). Going beyond that in both deflection angle and angle of attack will need a reduction in flap effectivity which can (in extreme cases) even become control reversal.
Also note that the aileron especially will twist the wing such that its effectivity is reduced at higher dynamic pressure. The details of this effect depend on the stiffness of the wing.
Your example of a NACA 0024 is already so thick that it will not tolerate big flap deflection angles and show separation on the suction side. Good wing thicknesses for subsonic flight are between 12% and 15%, and the most extreme ones (like the root of highly loaded high aspect ratio wings) will still be below 20%. Supersonic wing thicknesses are generally between 4% and 6%.
If you depend on that control surface for trimming the aircraft, don't let its effectivity decrease (as it would in reality), but give it linear effectivity (without the sine function) into infinity and punish large deflection angles with excessive drag (or whatever runs against your target parameter).

Wonderful! This is quite a bit to run with. TBH I just picked 0024 to start with because it was easy to make a 3D model of, and 'reads well' on screen.  Thanks again for all of the helpful information!

@Habitablaba: Just one detail: Make sure you do not use the percent value of d in the root, but the fraction. Also, I forgot the lift curve slope. Sorry for the wrong description, this was not my day!


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How many miles before the runway should an airliner put the gear down?
I was watching this video of a FedEx MD-10 landing and some questions came up, of course again the unprofessional YouTube comments didn't help.

How many miles before the runway should an airliner put the gear down?
Was the aircraft in the video too close?
At which distance does radio altimeter warn the pilots?
Is the following YouTube comment accurate?

This was FedEx flight 1356 and I can tell you what happened. During approach there was an anomaly on the left slat and it was being watched. Also during approach engine no.1 was heating up to unacceptable levels and because of all of this the gear wasn't lowered right away. It was only due to TCAS and the alarms on board that it was noticed as the aircraft was approaching it's minimums. Upon landing the crew was reprimanded for not following proper procedure and was suspended with pay.

TCAS doesn't warn the pilots for gear up approach (incorrect landing configuration); it's the radio altimeter that does.

Similar, if not duplicate: When do pilots deploy landing gear?

I'm not sure if this can be answered well. The general question about when to lower the gear has been answered already (see Farhan's comment); whether it was too close or not is speculation unless you know the aircraft's position and speed etc.; confirming whether or not Fedex disciplined the crew is difficult unless it was reported publicly, which is unlikely since the flight apparently landed safely; the question about the radar altimeter is good but kind of lost among the rest (this is one reason to ask only one thing per question).

It's not TCAS for the ground warning, it's the GPWS, Ground Proximity Warning System... or EGPWS, Enahanced GPWS.

The quoted comment contradicts the video's description about the flight number (description says 309, not 1356) and doesn't know what TCAS is for. Seems unlikely that the rest would be correct.

To answer the last part of your question, as ratchet freak said, the TCAS doesn't warn the pilot when he should deploy landing gear. However, the ground proximity warning system/terrain avoidance and warning system (GPWS/TAWS) does. GPWS Mode 4A is "Unsafe Terrain Clearance With Landing Gear Not Down".
If the plane is less than 700ft (based on the radio altimeter's measure) high and under mach .35, there is an aural alert in the cockpit saying "Too low - gear". The message is repeated until the situation is corrected.
So the warning is based on the height and speed of the aircraft. Not on its distance to the airport.

bonus points for saying 'height' and not 'altitude'

In cases where the airport is on top of a hill, would it also warn when you're below a certain height above the runway altitude or does it rely solely on the radio altimeter? For example, in the GA airport where I've done most of my flying, the runway sits on top of a ridge and there's a 400 foot drop very close to both ends of the runway. In such a case, would it potentially fail to warn you until you're almost right on the runway?

@reirab The enhanced GPWS (EGPWS) is also available with a GPS. In this case, it can be set up to warn the pilot based on a airport terrain database and the GPS position, as to prevent the kind of situation you describe.

...so if the plane is less than 700 feet AGL with gear up, but is travelling faster than Mach 0.35, they won't get that warning?

As people have said I the comments there is no general rule as to when to lower the gear.
All major airlines have Standard Operating Procedures. As part of the Normal Procedures Section there will be profiles for the different types of approaches (ILS, GNSS, VOR etc..). It's normal as part of these to show the recommended config of the aircraft at a particular stage of the approach.
An example would be to lower the gear when capturing the Glide Path as part of an ILS approach. This aids speed control and ensures the aircraft is stable at the required minima.

another good reason for putting the gear down at glide slope intercept is that it requires only one power change instead of two to stay on Vref (one power change intercept to begin the descent, and another power change when the gear is deployed).

Well, there is some rule. The already linked answer indicates the before landing checklist (which includes gear down) should be complete by 500 ft above field elevation in VMC and 1000 ft in IMC; in large planes that react more slowly it should generally be 1000 ft always.

As I stated it would depend on the operators procedures. Which is what the linked answer refers to. There is no "general" rule as it is operator and type specific.


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Are there any heavy lift jets (like Stargazer) with zoom climb (like Ye-66A MIG-21)?
Are there any intercept jets (that can zoom climb like 1961 April 28 113,891ft Ye-66A Mig-21 Turbojet) built for heavy lift?  I see the Stargazer and Stratolaunch as really slow heavy lift vehicles that cannot zoom climb.  I saw one article about using an F15E as a rocket lifter.  Is it silly to dream of a purpose-built large jet that could carry a large payload (like a Pegasus rocket) and zoom climb to a high altitude (100,000ft) before releasing its heavy rocket payload?

Zoom climb of the carrier is useless. The rocket can do it alone after release with the same effect and is slightly more aerodynamic as it does not have the large wings of the carrier.
The rocket starts with certain amount of energy upon release. Part of this energy is kinetic, given by speed of the carrier, and part of this energy is potential, given by altitude. Now a zoom climb means exchanging kinetic energy from going fast for potential energy to climb higher. But the total amount of energy does not change. And since the rocket still needs to increase both it's kinetic and it's potential energy (accelerate and climb) it does not really care which form of energy it gets.
Now the orbital vehicle needs energy corresponding to 7.9 km/s and a launch aircraft like the Stargazer can give it perhaps 0.57 km/s (of which only ~0.24 km/s will be speed, the rest is the ~12 km altitude). This is a tiny fraction of what it needs, but:

It helps significantly that the rocket does not have to penetrate the thick low atmosphere. At 12 km the pressure is 19% of what it is at sea level. Going higher is not going to help all that much.
Due to the rocket equation (the amount of fuel needed is exponential) it can still make significant difference to payload fraction.

What we are likely to see is carriers that can give the orbital vehicle more initial energy. By going faster (like the F-15), by going higher (like the Stratolaunch) or both (using scramjets it to gain some higher hypersonic speed at altitude perhaps 30 km). But they won't do zoom climb, because that does not add any energy and adds complication.

Maybe it is not totally useless, if it helps to cut the flying time at high density by shifting the acceleration to higher altitude. The launch profile would be similar to that of a rocket, but now the first stage is airbreathing.

@PeterKämpf: But I don't see any difference between the launcher zooming and the rocket zooming alone just after release from the highest point where the launcher can still sustain flight. The energies involved are the same and the rocket alone should have lower drag (because it can do with smaller wings).


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For large jets, what is the primary means of slowing down after landing?
I understand that a large(r) commercial jet slows down after landing using the following methods:

Wheel brakes
Reverse thrust
Spoilers/flaps/airbrakes

What is the effectiveness of each compared to the others? What if one of the first 2 fails? Can an airliner usually be stopped without using wheel brakes or without using reverse thrust?
And what if the runway is slick because of rain, snow or ice? Does that change the equation?

The brakes are much more effective than anything else, at least for the jet I have experience in (EMB-145).
Our landing performance data typically assumes full braking application, spoilers deployed and no reverse thrust.  The airplane will most certainly stop without using reverse thrust, just not as fast.  I never tried not using the brakes, and if I were to I would want a light airplane and a very long runway.
As Lnafziger pointed out in the comments, the brakes are part of redundant systems so that they are always available.  In the EMB-145, the brakes were serviced by two independent* hydraulic systems. The inboard brakes were on one system while the outboards were on the other for a total of four wheels each with big carbon fiber brakes.
To address the comments on slick runways, assuming braking action allows an attempt to land in the first place, you have to be careful. With reverse thrust alone you may not be able to maintain the runway centerline and directional control may become difficult through uneven deployment of the reversers and other factors.  In this scenario the spoilers are helpful to increase traction and brake effectiveness.  In short, if the runway is slick then the only way I'm attempting a no-wheel-brake landing is after declaring an emergency.
Finally, to address the question in the title, the wheel brakes are always the primary means of slowing the airplane.
*You could transfer fluid between our systems through the parking brake.

As far as light airplanes are concerned, I guess it depends on how light you're talking about. If you're talking about a light jet, then, yes, you'd need a very long runway. However, for light prop aircraft, it's easy to land without brakes. At the airport I usually fly out of, even if I don't brake at all, the Cherokee I've been flying would stop before I get to the taxiway to exit the runway if I didn't add power first.

Just because the brakes are redundant does not mean they are always available

Perhaps instead of thinking of a single primary means of slowing a large jet, we should think about a primary means for a given set of conditions, the combinations of which are numerous. To mention a few: What is the weight of the aircraft. Passenger aircraft are typically nowhere near max landing weight when they land. Freighters are often loaded such that they may be very close (or even over truth be told) to max landing weight. Is the aircraft going to be on the ground a sufficient time for brakes heated to their max to cool? Was the leg from which you are landing long enough to allow the brake and tire energy from the taxi and takeoff to dissipate? Is where you're landing used to having to handle hot brakes and thus can be expected to have a huffer readily available to cool them and people who know how to do it? Do you have a reverser locked out for maintenance. Does your next departure allow for safely leaving the gear down for awhile and thus gave you more leeway on heating the brakes when you landed.
Just some thoughts.

This video on YouTube shows a 777 in certification trials, accelerating at maximum gross weight from standing start to $V_R$, then stopping with maximum brake pressure and no reverse thrust. The brake discs are also ground down to the minimum thickness permitted by the maintenance manual to simulate the worst case scenario.
The brakes get white hot!  Then the plane has to taxi for 5 minutes, before having the fire department cool the brakes.  The test is to ensure that the brakes can handle the maximum load as certified, and secondly that the brakes do not catch on fire and incinerate the airplane.
If the runway is slick it just takes longer to stop.  Thrust reverse will help significantly in this case.  Thrust reverse is prohibited below a certain speed because the reverse thrust will kick up FOD which the engines may suck in, causing expen$ive damage.  However, in an emergency, thrust reverse will stop the plane.

Reverse thrust below a certain airspeed not only kicks up FOD, but it also causes turbulent and warm exhaust air from the engine to get sucked back into the engine. This can cause a compressor stall.

Watching them stand so close to the extremely hot tires while they rapidly cool them down seems crazy to me.

@zymhan Most (all?) airliner tires have fuse plugs that will melt at high temps. This will prevent the tire from blowing up (details here). If you note, the emergency personnel will stand in front of or behind tires, not next to them. This ensures they're out of the line of fire if the fuse plug blows instead of melts.

While landing you want to reduce speed for which you need spoilers and to have more lift and drag you have the Flaps deployed than just when you touch down on runway ground spoilers are deployed. If want to land with short runway length then you go for reverse thrust (nice to have in normal scenario but in case of emergency it can be a life-saver). Then we need wheel brakes to stop the plane.
Effectiveness:

When in air/near ground: only spoilers/Flaps and airbrake (ground spoilers) are effective to reduce speed of aircraft but not to stop it
Flap are required to keep the aircraft in a configuration such that you don't crash on ground
When on ground: you still have airbrakes/spoilers effective when aircraft speed is high but its effectiveness decreases at low speed. So, are other control surfaces useless @ low speed (Flaps/Spoilers etc). Reverse thrust and wheel brakes are the one you can rely on.

Failures:
All critical systems on aircraft have redundancy so the probabilty of failure is around 1e-8 /flight-hr but still you never know. I think you will be able to land but you need more runway length in case of two fail scenario.
Yes, I believe you can land without wheel brakes by using reverse thrust but purpose of reverse thrust is only to reduce aircraft speed such that we land on short runway. so, its not recommended to not use wheel brakes and use reverse thrust.
Slick runway/rain or snow on runway has same effect as it has on other land vehicles.. Aircraft will take more runway length than usual.

plain and simple: the brakes. Reverse thrust is much less effective than brakes. And that's just talking about the force to slow down, not even taking into account that jet engines need a few seconds to spool up (6 or more) and brakes are effective immediately (perhaps 1 s delay).

I have landed at Cabinda and Angola.
I have made many landings there. They can be tricky, but local pilots use CPP, reverse thrust and wheel braking.
One pilot has mentioned that disc pads are very expensive, so you want to wear them down as little as possible.
The same pilot mentioned that reverse thrust can also damage engines, no matter whether CPP or jet engines.
I am still flying cessna's.

I tried to clean up grammar and spelling.

This does not seems to be an answer, it gives some opinions on the stopping methods, but does not answer the question what is the primary mean of slowing down after landing?


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How does VDL relate to ACARS and CPDLC?
I know that ACARS and CPDLC are 2 different systems, so I can compare ACARS vs CPDLC, but can I do the same comparation between CPDLC vs VDL? Or a CPDLC it’s a VDL?
If CPDLC it is a VDL, ACARS it is a VDL also?

@ymb1 In the context of aeronautical communication, VHF and HF often equates "analog voic transmission over the VHF.HF band", while VDL and HFDL are the support for digital in those radio bands (DataLinks). So ACARS and CPDLC does not use VHF nor HF.

Also, not a duplicate of this particular question.

The question is about confusion between the layers in the OSI model. VLD covers the lower two layers and a bit of layer 3. ACARS and CPDLC cover higher layers and work on top of various implementations of the lower layers. Voted to reopen.

TL;DR : according to the most usual meanings of these acronyms :

ACARS and CPDLC are applications
VDL is a point-to-point communication technology

To give an everyday-world analogy, the relationship between VDL and CPDLC/ACARS is the same as the relationship between 3G/4G and the web browser/facewhatstime app of your smartphone.
More detailed answer
From a telecommunication point of view, we represent the different functions of a network by different layers. Ideally, one can replace the technology used to implement a given layer by any equivalent technology without impacting the other layers.
The VHF Data Link (VDL) is a technology used to implement the functions of the physical and datalink layers. It means that it is a technology designed to carry any digital data directly from one "device" (aircraft or ground station) to another (resp. ground station or aircraft), independently of its actual content. There are different versions of VDL, namely modes 1 to 4. The current deployments of VDL in europe by ANSPs use VDL mode 2.
CPDLC is an application (application layer). It is directly facing the user, and can use any layer below it (in particular, it can use VDL, HFDL or satcom as layers 1/2)
ACARS is ... a more ambiguous word. It predates the OSI model, and at first it described both the application (text-oriented transmission) and the point-to-point communication technology. Nowadays, pilots use the word ACARS to talk about the application (the printer in the cockpit), and that particular application can, as any application, use any underlying link layer (VDL, HFDL, satcom...). But the old meaning of "ACARS" to describe the original blob of "point-to-point  technology + network + application" can still be found today, for example in the acronym POA (plain old ACARS). By the way, the  point-to-point technology originally used by ACARS is also called VDL mode 1.

Many thanks for the reply!
It helped me a lot, but if possible I would like to ask another question. If this is outside from the regulation, I apologize.
My question is, if ACARS is VDL MODE 1, why is it still in use?
From what I researched, ICAO removed the standards from VDL mode 1, in this way I interpret that VDL mode 1 is prohibited for aeronautical use.
But I still see that ACARS is in use, so I still confuse about it.
Thank you very much!

@MaximilianKaden Nowodays, when someone talks about ACARS, they (most likely) talk about the application (the printer that is aboard aircraft). This application can use any underlying data link : VDL(2-4), satcom...

Humm, I asked that because I all the time read a lot of books saying that
"VDL Mode 2 has a much higher and faster data capacity than the existing ACARS."

That confusion is quite common (see how your question was at first seen as a duplicate), even (especially) amongst people familiar with civil aviation. That's why I wrote that using the word ACARS is often ambiguous. In your books, they are certainly referring to the capacity of the original datalink used for ACARS, and they do not make a clear distinction between applications and the underlying data transmission technology.

This confusion is especially common in civil aviation because, for a long time, a new system requiring communication meant systematically adding a new transmission device (with its antennas, allocated frequencies...). With new digital services, the distinction between the different OSI layers becomes necessary, hence my answer.

And for the record,  "VDL Mode 2 has a much higher and faster data capacity" : 31.5 Kbit/s. It is 10000 times slower than 4G.

Humm, I'm still confused, I found in my EASA Books this statement
"ACARS is gradually being replaced with VDL mode 2 which provides a digital link at a rate of 31.5 kbps, giving more than 10 times the capacity of ACARS. VDL mode 2 requires specific address for an aircraft and the unique mode S address will be used. This type of digital system is known as controller pilot datalink communications (CPDLC)"

This citation is a perfect illustration of what I was saying (the lack of distinction between the different OSI layers when civil aviation people are talking), and how confusing it is when you try to understand things in depth. The last sentence is misleading, and may indicate that the author does not make clearly the distinction between the application and the underlying layers.

To repeat myself: CPDLC is an application that rely on a datalink. VDL2 is a datalink that can handle CPDLC, as well as other applications.

Anyway, if you go by the EASA book, you will be as right as most of the people who work in civil aviation. I have met quite a few of them, and this confusion is very common (with the exception of network specialists). I am probably nitpicking, but I think that learning things correctly will help you. My conjecture is that datalink will be used in the future for other things than controller-pilot communications, so people will need to make that distinction sooner or later. If it is not too personal, could you tell me in which context you need this information ?


text:
Maintaining straight and level altitude
just a completely random question that I suddenly thought - doesn't straight and level flight prove that the earth's surface is not a globe? Once cruising altitude is reached, the plane remains at the same altitude for the entire flight until it starts to descend for landing. If earth was a globe, we would need to drop the nose of the plane every couple of minutes to compensate for the curve of the earth. Is this correct? Because on my most recent flight, we reached 2000ft altitude and my instructor told me to maintain this altitude for 30 minutes (which I managed to do). I asked why we don't need to compensate for the curve of the earth and he couldn't answer me. Sorry for the random question but it's been bothering me.

I would say off topic as this is about debating whether earth is round using airplane.

@757toga please try to avoid to provide answers, however partial, in the comments.

All else aside, unless you have a REALLY fast airplane, you won't travel far enough in a couple of minutes for the curvature to be noticable.

Just observing that the exact same principle applies to ships on the sea.

Set aside the barometric stuff.  The simple answer is that what we think of as altitude, on a sphere, is really distance from the gravitational source, the center of the sphere.  Therefore, a "constant altitude" is not maintaining the same plane in 3 dimensional space, but the same distance from the center of the earth.

Once cruising altitude is reached, the plane remains at the same altitude for the entire flight until it starts to descend for landing. If earth was a globe, we would need to drop the nose of the plane every couple of minutes to compensate for the curve of the earth. Is this correct?

You're right, except for one thing: the "every couple of minutes" part.
Since the earth is a globe, aircraft need to pitch down in order to maintain a constant altitude. So, for example, if an airplane makes a flight which covers a 15 degree arc across the earth's surface (which is a distance of about a thousand miles), then the airplane will need to pitch down by 15 degrees over the course of the flight.
However, in order to accomplish this, pilots don't "drop the nose of the plane every couple of minutes". Instead, they watch the altimeter, and raise or lower the nose as needed to maintain a constant altitude, or to climb or descend as necessary. (Or they set the autopilot to do the same thing.) This means that they're adjusting the plane's pitch every couple of seconds, and the adjustments that they use to maintain altitude are much, much larger than the adjustments that would be needed to merely match the curvature of the earth.
The short version:
Question: Why don't pilots need to pitch down occasionally in order to follow the curvature of the earth? Answer: They do.

It looks like this answer has been downvoted, but I'm not aware of anything wrong with it.


text:
On a constant speed propeller, how is blade pitch related to airspeed and efficiency?
I'm trying to wrap my head around what the PHAK (Pilot's Handbook of Aeronautical Knowledge from the FAA) states for constant speed propellers.
First, why is it that if airspeed increases, for a fixed RPM, your blade pitch will increase, and conversely decrease if airspeed drops? Is it because it wants to maintain that low AOA (2-4 degrees according to the PHAK) with the relative airflow? If its AOA were to increase, such as not changing blade angle as airspeed drops, would drag increase causing the RPM to fall? And if airspeed is too high and AOA is too low, there's not enough drag to slow down the blades?
On takeoff, you want max thrust/power. By setting the blades to low pitch, you get max RPM because the blades take less of a bite out of the air. This also keeps blade AOA low which in turn reduces drag and allows RPM to build? Also, is max thrust in this case the result of the blades generating a lot of lift because of their high velocities from the higher RPM (versus thrust from moving larger chunks of air)?
Why is low RPM preferred in climbs/cruise? If you increase the blade pitch in these flight regimes, you get a smaller AOA with respect to wind which from my understanding so far reduces drag? But then doesn't the blade taking larger bites of air require more power anyways to maintain that RPM? Is it more efficient to give power to blades to move larger loads of air than it is to run at lower blade angles and higher RPM?
And lastly, with regards to blade AOA and relative wind, would a blade generate more lift if it had a higher AOA, but at the expense of additional drag on the blade which in turn requires more engine power? Is this drag induced drag because it's an airfoil?

Welcome to aviation.SE! We have a few questions that might help, especially this one and this one. And the [tour] may be useful if you're new to the site.

Thanks! The first one helped clarify it a bit. But do you know why, from a physics standpoint, we're able to impart less energy into the air and still get the same forward acceleration? It seems like theoretically, to have X amount of force work against drag, you need X amount of energy. How can you justify from an energy/math standpoint a higher angle blade uses less energy?

Can you maintain highway speed  by shifting up gears and easing off on the gas? Twisting the prop more at cruise altitude while slowing down the RPM has the same effect.  If you want to accelerate to pass someone, you step on the gas and sometimes downshift. Same with cruising faster or climbing - back off the prop twist and increase the RPMs.

Ok so what you're saying is you can't achieve high thrust with large blade angles but level flight is not a problem? When you need that extra kick in thrust you need more RPM which leads to higher energy use?

Yes. You can pull back on the stick (yoke) to start the climb; the prop governor will work to keep the engine RPMs the same, while the higher twist will keep you bogged down. To keep on climbing, you add more thrust and dial back the propeller pitch to allow more horsepower, effectively downshifting and stepping on the gas to stick with the car analogy.

@Flak , in my opinion, It would be more informative and clear for readers, if you would split 10 different question in your post and ask them separately. Otherwise, very interesting subject.

A propeller has an optimum AoA, where the thrust/drag ratio is highest. A variable prop can maintain this optimum AoA at a wide range of speeds, thereby reducing fuel consumption. That's all it does.
Fixed wing propellers have a dilemma that at take-off they require maximum thrust, and in high-speed flight the engine will need to be throttled back to prevent overspeeding. Maximum engine power cannot be utilised at every airspeed.

why is it that if airspeed increases, for a fixed rpm, your blade pitch will increase?

To maintain optimum blade AoA. Increased airspeed causes reduction of blade AoA at constant pitch.

On takeoff, you want max thrust/power.

You want maximum thrust. This is generated by making the propeller spin as fast as possible (not exceeding tip Mach), with a maximum blade pitch where the blade does not stall. Reducing blade pitch to increase RPM results in no increase in thrust: Power = Thrust * RPM.

If you increase the blade pitch in these flight regimes, you get a smaller AOA with respect to wind

No a larger AoA. More thrust and more torque on the propeller axis.

Is it more efficient to give power to blades to move larger loads of air

The engine runs most economically at the RPW where maximum torque is generated, the constant speed propeller speed control wants to maintain that RPM.

would a blade generate more lift if it had a higher AOA, but at the expense of additional drag on the blade which in turn requires more engine power? Is this drag induced drag because it's an airfoil?

Yes and yes :)

Ok, and so as you increase airspeed, you want to increase pitch to maintain optimal AoA? Why does reducing pitch to increase AoA not increase thrust? In climb/cruise, do you need overall less thrust hence why you don't run at high RPM? What do you mean by an RPM where max torque is generated? Is torque not proportional to engine power?

@Flak, this is more engine properties than propeller properties. RPM limit power, so you need higher RPM for higher power, but it causes more engine wear, so you want lower RPM when you don't need as much power. Piston engines start losing torque beyond some RPM as the charge takes longer part of the stroke to burn through, leaving smaller part for the expansion that does the actual work, so there is RPM where the torque is highest and there the engine is most efficient. Turbines would have similar effect as the turbine blades have fixed pitch, but are usually more limited by wear.

@Flak, for propeller efficiency, if you keep high RPM for low power, the blades fly at too low pitch and generate relatively too much parasite drag for the lift, so you want to reduce RPM when you reduce power. But if you try to put too much power at slow RPM, the blade pitch will raise too high and the blades will run at too high pitch, generating too much induced drag or even stalling. So for the propeller, the optimal RPM is also proportional to power.

Ok so at cruise, you set RPM based on what you want your power setting to be to both maintain speed and be efficient by balancing induced to parasite drag. This is done by the correct AoA on the blades, which have a preferred most efficient AoA right? Also is torque and power not synonymous? Just because you have more power it doesn't necessarily mean more torque? And blades spinning slowly bc of high AoA and low RPM on takeoff can't produce enough thrust bc despite their high AoA they don't have much velocity right?

Also. For fixed pitch propellers. Is your max speed limited because your blade AoA will become ineffective at too high forward speed as relative wind changes direction? So it can provide high enough thrust to overcome drag?

@Flak Power consists of both torque and RPM. In specifications for car engines for instance, it states a max power (@max RPM) and a max torque at a lower RPM. In the higher RPM regions, torque decreases but torque * RPM increases due to increase in RPM.

Yes fixed pitch propellers stop providing thrust when the local AoA reaches zero. The constant speed prop keeps adjusting the pitch.

@Koyovis Is that why having a high AoA blade on takeoff is foolish? Because you're using so much torque because of that higher AoA and getting little RPM out of it? And since you have slow relative wind, that high AoA doesn't give that much lift?

Only having too high a blade pitch would be foolish. High AoA results in high thrust and high required torque, and the engine can spin it up to the maximum power limit. Try to go above that by demanding more blade AoA, and the torque demand is too much for the engine and RPM reduces => thrust reduces.

@Flak, keep in mind that a constant speed propeller means that you select the desired RPM and the governor selects the AoA at which the engine can spin it up to that RPM. On take-off you need power, so you need to set high RPM, but the AoA still comes out moderate, because the engine is producing a lot of power. And then the pitch increases as you accelerate to compensate for the relative wind, but the AoA stays about the same.

An important thing to keep in mind is that the propeller control system has no idea what the blade angle is (except in BETA mode systems which is another topic completely).  It's a flyweight governor that just moves the blades coarser, finer, or holds them static based purely on engine speed, and the speed setting from the prop lever is just increasing or decreasing pre-load on a spring that tends to hold the flyweights in.
The governor just knows: Speed too fast, flyweights move out, routes pressure to move the blades more coarse; speed too slow, flyweights move in, routes pressure to move the blades more fine.  How coarse or how fine, the governor does not know or care.
A specific blade angle and AOA is a function of the torque the engine is producing and the speed setting.  There will be some optimum AOA at any one time, but since we can't control that specifically, we are only concerned with RPM and let the blade angle take care of itself.
Since total HP is a function of manifold pressure and RPM, I can use a range of different engine speeds and throttle openings to make the same HP.  There will be a speed/MP setting that roughly results in blade angles that are optimal when making say 85% power and this would be the recommended power setting for 85% power climb (typically something along the lines of 25" and 2500 RPM say).  But I can use a lower RPM and higher MP to make the same horsepower if I wanted, such as 2400 RPM and 26", still making 85% power (I'm just pulling numbers out of my head for illustrative purposes here).
There is an old saw that says "oversquare" settings (low RPM/high MP) like that are bad, but it's not really true unless it's taken to the extreme.  There is a benefit to using lower RPM, such as 2100 RPM and 25" MP vs 2300 and 23" to make the same HP, because the engine most benefits from slowing down all the reciprocating parts. Less friction and therefore less heat, and very importantly, piston ring speed, and distance traveled, is less for a given power setting (piston rings wear out based on distance traveled; slow them down and they don't go as far per unit of time). Cylinder internal pressures are higher running oversquare, but unless temperatures are high or there is detonation (a potential only at the extremes, like WOT at min RPM) it's not important (supercharged engines spend their entire lives crazy oversquared).
Operationally, it's the power and RPM that's the main concern, not optimizing blade angle.

Another good reference is this McCauley booklet in which

Professor Von Kliptip Answers
  Your Questions About
The McCAULEY CONSTANT
  SPEED PROPELLER
  GOVERNING SYSTEM
FOR NON-COUNTERWEIGHTED PRESSURE
  TO INCREASE PITCH PROPELLERS ON
  TYPICAL SINGLE ENGINE AIRCRAFT

Reading it, one can see the method of spring/flyweights/oil pressure controls the piston that determines the amount of blade twist.
Onspeed, Underspeed conditions and overspeed conditions described on pages 10, 11 discuss how constant speed (RPM) is maintained in climb and descent conditions.
Sorry, I don't see a way to attach it, you'll have to deal with the link. Page 6 on the left and 7 on the right let you see the whole diagram presented.
https://www.airtreknorth.com/uploads/4/7/2/4/4724302/von_klip_tip_cs_propeller.pdf
(prints best on 8.5 x 11 when scaled to fit to page).

Take a look at page 148 from Aerodynamics for Naval Aviators, a great book freely available.
https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/00-80T-80.pdf
This picture from the book shows how prop efficiency is related to blade pitch and advance ratio (which is proportional to speed). The top shows how it varies for a series of fixed pitches.
The bottom part shows how prop efficiency varies for a constant speed prop, which shifts $\beta$ to absorb the power coming out of the prop, resulting in a blade position that is ideal for that particular speed.

The ideal efficiency curve for the constant speed prop can be shifted through the prop design, with the peak efficiency in the plot potentially designed for a takeoff condition, cruise, etc.
Also note in the bottom plot how thrust varies with advance ratio (it shows speed on the horizontal axis, but it is really advance ratio). For takeoff or landing, where you want maximum thrust available and are willing to sacrifice efficiency for a period of time, you'd like to run the prop at a low advance ratio. It naturally happens that as you slow down the advance ratio lowers, but you can further decrease it by increasing the RPM if you have an engine where the engine and prop RPM are not directly coupled (e.g., turboprop with an N1 and N2 turbine). If you've flown on a Dash-8, you'll note how they use a higher RPM for takeoff and landing, and a lower RPM once up and away. More thrust available in the landing pattern, more efficiency in cruise.


text:
What is the meaning of this "Navigational Warning" and does it apply to the aviation industry?
This was posted at https://sattrackcam.blogspot.com/2021/09/an-upcoming-trident-ii-d5-slbm-test-in.html
Th blog post notes something as a "navigational warning".

A few days ago a Navigational Warning (NAVAREA IV 838/21, also
issued as HYDROLANT 2336/21) appeared

And it says that the warning mapped to a upcoming missile test. (check the link)
The text is this:

151459Z SEP 21
NAVAREA IV 838/21(11,24,26).
ATLANTIC OCEAN.
FLORIDA.

1. HAZARDOUS OPERATIONS 171230Z THRU 200123Z SEP
   IN AREAS BOUND BY:

   A. 28-56N 079-59W, 29-02N 079-53W,
      29-06N 079-37W, 28-59N 079-10W,
      28-37N 079-10W, 28-36N 079-35W,
      28-45N 079-56W.

   B. 28-24N 076-44W, 28-42N 076-42W,
      28-21N 074-40W, 28-06N 074-44W.

   C. 27-27N 071-21W, 27-52N 071-15W,
      27-25N 068-46W, 26-54N 068-54W.

   D. 17-22N 044-54W, 18-33N 044-32W,
      16-54N 040-55W, 16-00N 041-23W.

   E. 09-00S 003-51W, 08-22S 003-22W,
      12-35S 002-40E, 13-05S 002-19E,
      11-56S 000-16E, 12-09S 000-16W,
      11-34S 000-20W.

2. CANCEL THIS MSG 200223Z SEP 21.

Is this a threat to planes? Do pilots and/or other relevant bodies consider this?

@ymb1  for people sailing or flying in that part of the world. read the answer.

@ymb1 you are saying that this is offtopic? : is this a threat to planes? Do pilots and/or other relevant bodies consider this? also threats doesn't need to have altitude information such as terrorists with arms.

@ymb1 It is the warning, I specifically asked the pilots do they consider it. I removed the parts which will be off-topic because only now I know it is for maritime.

@ymb1 Why would that's what I am asking. why part comes part do.

@ymb1 does it say it's used by pilots I don't say it is used, that's why I asked do they.

To be clear - neither I or, nor any other pilots I know, reference the Navigational Warnings promulgated by WWNWS. This is the first I've ever heard of them. It is standard for pilots to reference TFRs and NOTAMS, with other lookups based on where you're going. TFRs and NOTAMS do cover missile launches, like the one you referenced.

@ymb1 If it wasn't for the edit invalidates the answer I might have written a lengthy Meta post Why some of you are illusion-ed in the matter of offtopic.

It looks like a warning for people sailing or flying in that part of the world. Google says:

Navigational warnings (NAVWARNs) contain information for boaters about
changes to navigational aids and current marine activities or hazards,
such as: defects. dredging.

The latitude and longitude points will show you exactly where expected danger is expected to occur. It has a map in the article you linked - what else would you like to know about what parts are dangerous?

I updated the question.

Where does google say about flying?

Google didn't say anything about flying, but if there were an ICBM test I certainly wouldn't fly inside those boxes.

"Google says [...]": To be fair with the content author, it's not Google which says that, but the Maritime Safety Office, https://msi.nga.mil/NavWarnings. Google just cites it.

There might be a corresponding NOTAM -- notice to airmen, which warns fliers to avoid this area.  It also might be inside a published warning area, which would simply "go hot" around the time of the launch.  So there are ways that pilots get this sort of info, but the document in the OP is not it.


text:
If you are able correct your vision in one eye, must you correct your vision?
After reviewing this exchange: Can you obtain a pilot license with impaired vision / being blind in one eye?
I can see that having monocular vision is allowed by faa rules, but I would like to clarify a specific situation if possible.
For 30 years I have had correctable vision in one eye after having the lens removed due to an accident. I do not like or want the correction, but I had a driver's license examiner try to tell me that if my vision could be corrected, then it had to be corrected
So would the FAA medical examiner say that one can't fly without correcting their vision as much as possible, or just allow them to pass off as monocular? What if someone with perfect vision just liked wearing an eyepatch while flying?
Details: L eye 20/15, R eye 20/2000, correctable to about 20/40.

What kind of flying are you thinking of? Private or commercial? Not sure if it makes any difference though.

Were the glasses too uncomfortable also?

@vasin1987 both eventually.

@jpe61 glasses would have an inch thick lens in one eye, and nothing in the other.

Oh man, now I get it!

FlightPhysical.com

An individual with one eye, or effective visual acuity equivalent to monocular, may be considered for medical certification, any class, through the special issuance section of part 67. (14 CFR 67.401)

Although it has been repeatedly demonstrated that binocular vision is not a prerequisite for flying, some aspects of depth perception, either by stereopsis or by monocular cues, are necessary. It takes time for the monocular airman to develop the techniques to interpret the monocular cues that substitute for stereopsis; such as, the interposition of objects, convergence, geometrical perspective, distribution of light and shade, size of known objects, aerial perspective, and motion parallax.

(14 CFR 67.401)

At the discretion of the Federal Air Surgeon, a Statement of Demonstrated Ability (SODA) may be granted, instead of an Authorization, to a person whose disqualifying condition is static or nonprogressive and who has been found capable of performing airman duties without endangering public safety.

The point of a SODA is to legally codify that ability through examination. At that point the holder of the Statement has satisfied the requirement and does not need to satisfy it in some other redundant way, as with corrective lenses.

"It takes time for the monocular airman to develop the techniques to interpret the monocular cues that substitute for stereopsis" I would think that the OP could argue that, having lived with this for 30 years, he's had the time to develop the techniques. I doubt he walks into doors very often because he just couldn't tell how far away they are. (Pointing this out for the benefit/use of the OP, not attempting to correct anything in the post.)

I suppose that will have to be good enough, each individual examiner would potentially have an opinion on it, but nothing in the rules addresses this. Thus, even if there were a judgement that I get correction, it could still be appealed, potentially.

@JuuB406 Examiner opinion has nothing to do with this. Obtaining a SODA means you legally satisfy the requirement. Do you expect the rules to say that you don't have to satisfy every requirement twice?


text:
What are the effects of missing questions on an FAA Written exam?
I took my Instrument Rating written exam this morning and scored an 85% (which is 51/60). Not bad, but I am worried about what this might bring about in the future. If I remember correctly for my private written, I got a 73%, and not only did I have to review everything with my instructor, but the DPE asked a question from every category I missed. Should I expect the same from my instrument DPE? That wouldn't be too big of a hurdle. The main thing I am worried about is the distant future. Do airlines have access to these scores?

Your question isn't clear. Are you asking if airlines have access to your score, whether they look and if it may matter?

I suppose yes... sorry I will edit

An airline wants to see that you have the ratings and the hours, which is demonstrated by your certificate, and your logbook.  While a logbook may be scrutinized, I've never heard of an airline having any way to find out what your score was on your writtens.  Heck, if they were to ask me, I wouldn't even have any idea what the scores were, nor where to research them.
Since the report on the exam is there with you at the checkride, it's not surprising that the DPE had access to that info, but once you're beyond that stage, you have the certificate, and so you met the standard, and that's the fact, end of story.
I wouldn't worry about the score.

Good to hear! Does the DPE really care either? The only thing my Private DPE said was "wow, you missed a lot." and then asked a question from each category and that was that.

I think the level of "care" that your Private DPE showed is about all you should expect.  You passed the written, and he's there to administer the checkride.  He can't bust you for the ground eval because of the score on the written, but he can use the categories to guide his questions somewhat.  Brush up on those categories in preparation for the ground eval, and you should be fine.

@TylerYoung The DPE is required to ask you at least one question for each area of deficiency to establish that you  addressed it. But they should hit all the key areas anyway; if you haven’t already, review the ACS to understand what to expect—and regardless of your score, be prepared to cover every single task listed.

Yes, the DPE cares and yes the DPE must test you on deficient areas (bolded for emphasis),

d. Airman Knowledge Test Report (AKTR). A designee conducting a
practical test must include the failed areas coded on the applicant’s
knowledge test report to evaluate possible deficiencies which may
affect the applicant’s flight performance. Designees are required to
have a current copy of the Learning Statement Reference Guide for
Airman Knowledge Testing to review the deficient areas identified on
the original knowledge test report provided by the applicant. The
instructor must endorse the applicant’s logbook, training record, or
bottom of the airman knowledge test, verifying that the applicant has
received the required training in the deficient areas.

The airlines will look for lots of things in a candidate. Your individual scores may not even be accessible (although you should keep the paperwork on hand). The bigger potential issue busting the whole check ride (forum link so take it with a grain of salt) as the airlines can see the discontinuance.